Enzyme and Transition-Metal-Complex Catalyzed Synthesis of Polyphenols with Pendant Oligo(p-phenylene) and Their Optical, Electrochemical, and Thermal Properties

Abstract

Horseradish peroxidaze (HRP)-catalyzed polymerization of 4-hydroxy[1,1′;4′,1′′]terphenyl (MonoPh(3)OH), 4-bromo-4′-hydroxybiphenyl (MonoBrPh(2)OH), and 4-bromo-4′′-hydroxy[1,1′;4′,1′′]terphenyl (MonoBrPh(3)OH) caused oxidative coupling at the hydroxyphenyl group to yield polyphenols with a pendant oligo-p-phenylene (OPP): PolyPh(3)OH and PolyBrPh(m)OH (m = 2 and 3; m − 1 denotes the number of pendant benzene rings). Polyphenols with a longer OPP chains (PolyPh(m)OH; m = 4 and 5) were obtained through the Pd-complex catalyzed reaction of PolyBrPh(m)OH (m = 2 and 3) with 4-biphenylboronic acid. The Pd-complex-catalyzed polymerization of 3,5-dibromo-4-methoxy[1,1′;4′,1′′]terphenyl or 3,5-dibromo-4-octyloxy[1,1′;4′,1′′;4′′,1′′′]quaterphenyl with 9,9-dihexylfluorene-2,7-diboronic acid bis(1,3-propanediol) ester or 2,5-dioctyloxybenzene-1,4-diboronic acid yielded polyphenylenes PolyPh(m)OMeFlu (m = 3 and 4) and PolyPh(3)OMePh, respectively, and hydrolysis of the methyl group provided polyphenylenes with the phenolic OH groups PolyPh(3)OHFlu and PolyPh(3)OHPh, respectively. Deprotonation of the OH group of the polyphenols with the pendant OPP obtained by the treatment with NaH caused a bathochromic shift of absorption maxima (λmax's) of the polymers. The bathochromic shift of the deprotonated species PolyPh(m)ONa (m = 3, 4, and 5), PolyPh(3)ONaFlu, and PolyPh(3)ONaPh increased with an increase in the donor numbers (DNs) of the solvents. PolyPh(m)OH (m = 3, 4, and 5), PolyPh(3)OHFlu, and PolyPh(3)OHPh were photoluminescent (PL) in solution. The emission peak positions of PolyPh(m)OH and PolyPh(m)ONa depended on the DNs of the solvents; that is, the emission colors could be tuned by changing the solvent. The polymers were electrochemically active in film.